Design & Analysis of Mono Composite Leaf Spring

Transcription

1 Design & Analysis of Mono Composite Leaf Spring R D V Prasad 1, R.Sai Srinu 2, P.Venkata rao 3 Asst.Prof 1, M.Tech Student 2, Asst.Prof 3 1 Asst.Professor Department of Mechanical Engineering, Bits Vizag, Andhra Pradesh, India. 2 M.Tech Student of Andhra University, Vizag. Andhra Pradesh, India. 3 Asst.Professor Department of Chemical Engineering, Andhra University, Vizag, Andhra Pradesh, India. ABSTRACT Leaf Spring is a critical load bearing element that connects wheel to the chasis in an automobile application. The Suspension leaf spring of one of the potential items for weight reduction in automobiles in order to achieve increased fuel efficiency and improved ride characteristics. The introduction of fiber reinforced plastics (FRP) made it possible to reduce weight of the product without any reduction in load carrying capacity and stiffness. Because of the material s high elastic strain energy storage capacity and high strength-to- weight ratio compared with those of the steel, multi leaf springs are being replaced by mono Leaf FRP springs. This paper deals with development of analytical formulation for Composite leaf spring and comparing the obtained results with the Conventional Steel leaf spring with 4 leaves. Composite leaf spring in this project has been developed as a mono block construction with maximum thickness at the center which is preferably glass fiber reinforced polymer. The thickness reduces towards the end in order to achieve uniform strength construction. The cross-section is constant at any section along the spring length. This condition is imposed to accoodate the unidirectional fibers and to maintain the fiber continuity from one end to the other. At first we designed a conventional Leaf spring with 4 leaves using ANSYS 11 and considered different loading conditions to obtain Stresses and Deflections. The dimensions of an existing conventional steel leaf spring of a light coercial vehicle are taken. Then we created a Solid Model of Composite leaf spring using CATIA V5 and imposed different loading conditions. Key words leaf spring, ERP springs, glass fiber reinforced polymer. I. INTRODUCTION A spring is an elastic body whose function is to distort when loaded and to recover its original shape when the load is removed. Though there are many types of springs, the following, according to their shape are important. The various applications of springs are to cushion, absorb or control energy due to either shock or vibration, as in car springs, railway buffers, aircraft landing gears and vibration dampers. To apply forces, as in spring-loaded valves and spring balances. To control motion by maintaining contact between two elements as in cams and followers. To measure forces as in engine indicators and spring balances. To store energy as in watches and toys. II. LITERATURE SURVEY JOHN E.MUTZNER and DAVID S.RICHARD[1] told in their paper titled Development And Testing Of Composite Truck Trailer Spring that, composite leaf spring constructed of glass fiber reinforced polymeric material have been recognized as a variable replacement for steel leaf springs since their introduction on the 1981 general motors covette. This acceptance of composite leaf springs has given rise to applications in high volume production passenger cars and utility of composite leaf spring is clearly demonstrated in these applications. This paper will discuss the design, laboratory testing, field testing, and development over the past three years that has led to the coercialization of the liteflex trailer springs. This will include the design process for high and low deflection composite leaf spring and stress analysis for coon springs used in various axle spacing worldwide. An explanation of laboratory test will be given and the rationalization for these test compared to steel spring test standards. An attempt will be made to correlate laboratory test tracks, servo hydraulic simulator and field tests of liteflex trailer

2 springs. This testing will demonstrate the soft failure mode if the composite leaf spring and the advantage this brings to fleet owners. The other advantage of weight reduction and increased durability will be discussed. KIKUA TANABE, TAKASHI SEINO[2] of Central Engineering Laboratories, Nissan Motors co., ltd. Yokosuka, Japan in their paper titled Characteristics Of Carbon/Glass Fiber Reinforced Plastic Leaf Spring designed and fabricated and evaluated a tapered leaf spring made of carbon fiber reinforced plastics. To construct the leaf spring, a carbon/glass fiber hybrid lamination is selected. This selection was made in concentration of chipping resistance, impact resistance and fatigue resistance. They constructed a prototype of leaf spring which weighed approximately 2kg included the front and rear steel eyes. In comparison with the steel spring, this represents a weight reduction of 76%. Prototype are put through a series of evaluations both on the bench and on the vehicle. As a result, the leaf spring proved to be better than the steel in such practical performance area as car handling and riding quality and endurance. III MODELLING OF FRP LEAF SPRING We have designed a solid leaf spring with all required dimensions as we calculated earlier. We designed this solid leaf Spring using CATIA V5 Software. FIG1. CATIA MODEL OF FRP LEAF SPRING 3.1 ANALYSIS OF FRP LEAF SPRING. The element used is SOLID 45(3-D four node tetrahedral structural solid with rotations). Solid 45 is well suited to model irregular meshes (such as pr oduced from various CAD/CAM systems). The element is defined by four nodes having six degrees of freedom at each node; translations in the nodal x, y, z directions and rotations about the nodal x, y and z directions. The element also has the stress stiffening capability. The SOLID 45 element can often be used in place of the SOLID 92 element to reduce the wave front and solution time. IV. NOMENCLATURE R- Radius of curvature of Arc M- Bending Moment acting at that point I- Moment of Inertia of spring section at the point y- Distance of extreme fiber from Neutral axis f b - Bending Stress b- Width P- Static load per wheel W- Laden weight of the vehicl d b - Bolt diameter 4.1 SPECIFICATIONS (passenger vehicle): Laden load - 14 tones Number of springs supporting the load - 4 Span of the spring Number of leaves - 4 Permissible deflection x10-6 Table 1 Mechanical properties of N155 & Inconel 718 SL.No Properties Value 1 Tensile Modulus along X direction E x, MPa 2 Tensile Strength of the 900 material, MPa 3 Compressive Strength of the material, MPa Mass density of the material, kg/ 3 5 Flexural Modulus of the Material, MPa 6 Flexural Strength of the Material, MPa 1200 V. RESULTS AND DISCUSSION

3 FIG2 NODAL DELECTION IN Z-DIRECTION FOR FRP LEAF SPRING FIG5 PRINCIPAL STRESS 2 FIG3 VON MISES STRESSES FOR FRP LEAF SPRING FIG 6 PRINCIPAL STRESS 3 RESULTS: STEEL LEAF SPRING FIG 4 PRINCIPAL STRESS FIG 7 NODAL DELECTION IN Y-DIRECTION IN STEEL LEAF SPRING

4 bottom part of the leaf spring. In the post processing, the results are viewed. Graphical display of displacement and stresses are shown in chapter 7. The main criteria of the design are obtained, but the structure is safe. The maximum deflection and maximum stress are found and it is shown in figures. VI FIG 8 STRESS IN THE STEEL LEAF SPRING DISCUSSIONS FRP leaf spring was designed in this work as a mono leaf constant cross-section area varying depth with fibers oriented in axial direction. The stiffness of the leaf spring must be so controlled that spring deflects to specified values during the bump ride so that shock will not be transmitted to the vehicle body. The leaf spring should have required fatigue strength to withstand the repeated loads arising due to bumpy ride. In this project, a procedure for designing a mono leaf composite leaf spring is formulated considering the constant cross section area. The thickness and width at various sections are calculated. Mono leaf FRP leaf spring is designed according to the given specifications for a truck. The three cases taken for calculating maximum load are: Case 1: vehicle passing over a bump while braking. Case 2: vehicle passing over a bump while accelerating. Case 3: vehicle passing over a bump while cornering. The designed FRP leaf spring is modeled in CATIA V5. Finite Element Analysis has been done in the created FRP model, for the maximum load of N. Here we used SOLID 45 element for the FRP leaf spring. First the leaf is meshed, boundary conditions are applied by arresting all the degrees of freedom in the eyes. Loads are applied in the Table 1 Maximum Deflection for FRP Spring S.No Load, N Ux, Uy, Uz, Table 2 Maximum Stress for FRP Spring Which are within the allowable limit.steel leaf spring is designed and modeled in ANSYS for the given specifications. Finite Element Analysis is taken out in ANSYS using the element BEAM 4 for the maximum load condition with same boundary conditions. In the post processing results are viewed and displayed in chapter 7. Table 3 Maximum Deflection for Steel Spring S.No Load, N Ux, Uy, Theoretical Deflection Table 4 Maximum Stress for Steel Spring S.No Load, N Line Stress Theoretical Stress N/

5 limit. The weight reduction has greater influence in noise and vibration characteristics. Glass fibers are for manufacturing instead of carbon due to low cost. The results are encouraging and suggest that ANSYS can be used effectively and efficiently in other complex and realistic designs often encountered in engineering applications, where experimental is not possible due to shortage of time and other constraints. VIII REFERENCE Fig 8 Load Vs Deflection Graph 1. W.G.GOTTENBERG and K.H.L.O IN THE 38 th Annual Conference, Reinforced Plastics/Composite Institute, The society of Plastics Industry, inc. February 7-11, 1983 titled Glass Fiber Reinforced Epoxy Leaf Spring Design. 2. JOHN E. MUTZNER and DAVID S.RICHARD titled Development and Testing of Composite Truck Trailer Leaf Spring. 3. Concepts and applications of Finite Element Methods ROBERT D.COCK 4. Introduction to Finite Element Methods TIRUPATHI CHANDRUPATLA ASHOK D.BELEGUNDU Fig 9 Load Vs Stress Graph Both the FRP and steel leaf spring are designed and modeled and results are compared: Weight of steel leaf spring = 347kg Weight of FRP leaf spring = 196kg Amount of weight saving = 43.5% Max. stress in steel leaf spring= 1247N/². Max. stress in FRP leaf spring= N/². 5. User Hand Book of ANSYS. 6. Introduction to Composite Material AUTAR K.KAW VII CONCLUSION & FUTURE SCOPE A procedure to design a composite leaf spring has been established. Leaf spring made up of E- Glass/Epoxy multi layered composites has been designed. FRP and steel models are created in ANSYS. The Finite Element Modeling presented in the analysis is able to predict the stress distribution. When maximum load is applied on the steel leaf spring, the maximum stress is greater than that of FRP leaf spring. Even under the maximum load, the maximum stress in the FRP is within the allowable